Abstract:

Avian influenza A H5N1 is a virus with pandemic potential. Mucosal vaccines are attractive as they have the potential to
block viruses at the site of entry, thereby preventing both disease and further transmission. The intranasal route is safe for
the administration of seasonal live-attenuated influenza vaccines, but may be less suitable for administration of pandemic
vaccines. Research into novel mucosal routes is therefore needed. In this study, a murine model was used to compare
sublingual administration with intranasal and intramuscular administration of influenza H5N1 virosomes (2 mg
haemagglutinin; HA) in combination with the mucosal adjuvant (39,59)-cyclic dimeric guanylic acid (c-di-GMP). We found
that sublingual immunisation effectively induced local and systemic H5N1-specific humoral and cellular immune responses
but that the magnitude of response was lower than after intranasal administration. However, both the mucosal routes were
superior to intramuscular immunisation for induction of local humoral and systemic cellular immune responses including
high frequencies of splenic H5N1-specific multifunctional (IL-2+TNF-a+) CD4+ T cells. The c-di-GMP adjuvanted vaccine
elicited systemic haemagglutination inhibition (HI) antibody responses (geometric mean titres $40) both when
administered sublingually, intranasally and inramuscularly. In addition, salivary HI antibodies were elicited by mucosal,
but not intramuscular vaccination. We conclude that the sublingual route is an attractive alternative for administration of
pandemic influenza vaccines.